I am not an expert but the encryption discussion is extremely important. Are you familiar with the Secure Email Lists (SELS) project? If not, drop everything and look at it at right now
http://sels.ncsa.illinois.edu/index.html
http://www.ncsa.illinois.edu/People/hkhurana/SAC05_1.pdf
To my limited understanding it seems to have the perfect solution for mailing lists. Instead of decrypting the messages and re-encrypting them, the mailing list server simply changes the keys needed to read the message without having access to the content of the messages. For this feat to be possible, the mailing list administrator receives the keys from the subscribers and re-issues a different key to each subscriber. I.e., the mailing list administrator must be a trusted person, but the server does not have to be trusted. I think this is often the situation with mailing lists. From skimming your messages I did not have the sense that you were discussing such a paradigm. Perhaps you are discussing it and I didn't get it, or you have good reasons not to. You don't have to reply to me if I am saying something obvious or stupid. But if you are not even familiar with this approach, I urge you to look at it.
Thank you for all the great work you are doing.
Hans G Ehrbar